a. Field of Invention
The present invention relates to hydraulic presses for compressing materials and, more particularly, to a modular press assembly which can be retrofit to an existing press or supplied as original equipment, in either case allowing multiple batches of material, of differing height, to be compressed with the same force, by the single press, in one operation.
b. Description of the Background
In various industries, it is necessary to prepare a mixture of ingredients in a compact solid body, having uniform size and shape. This is often the case where a measured amount of consumable material must be inserted into a chamber or other container, having a particular shape. Often, the ingredients are assembled in granular, powder and/or liquid form, to facilitate mixing. A binder is added and the mixture is pressed in a mold to form a solid body, of uniform shape comprising a homogeneous mixture of the ingredients. Shaped bodies of compressed material are formed by a pair of opposing rams operating on the mixture of material disposed within a shaped die, which is typically cylindrical but which may produce other shapes. The rams are operated by a press and exert pressure from opposite open ends of the die. Pressed density and consistent dimensions depend not on directly controlling the mechanical displacement of the rams, but mostly on precise control of the pressing force and amount of ingredients; even so, the finished height of the shape will typically have tiny variations.
In processing, for example, explosive molding powders, a relatively high pressure is required to achieve the degree of compression necessary to produce a body of the desired density and size. A set of matched, mechanical tools is required to process pressed explosives from a free-flowing molding powder into a precision, high-density consolidated shape. In its most basic form, this tooling set consists of a thick-walled cylinder (die), and two closely fitting pistons (press ram and eject ram). Typically, the tooling is installed in a double-acting hydraulic press, which has two hydraulic cylinders and guided platens. Both the upper and lower platens are moved by their respective cylinders and guided by a set of columns. The hydraulic press also has a center platen that does not move. Prior to installation of the rams and die, all three platens must be adjusted to be parallel to each other within 0.001 to 002 inches to facilitate the best possible axial alignment between the rams and the die. The press ram is attached to the upper platen, and the eject ram is attached to the lower platen. The die is attached to the center platen and does not move. The molding powder is poured into the die, the press ram is pressed down using a precisely regulated force, consolidating the molding powder, the press ram is retracted, and the eject ram pushes the resulting charge up and out of the die. FIG. 1 illustrates this basic tooling arrangement. Variations in the powder weight loaded into each die are a normal consequence of a production weighing operation. These produce varying charge volumes which manifest themselves in variations in finished pressed height. It is standard practice to place one die in the press and to use the press to produce one body at a time. Placing more than one die, in the press, is known as multiple position pressing. In multiple position pressing, variations in height among the positions will cause immediate asymmetric distribution in the press forces unless there is some mechanism to equally divide the press forces that can also accommodate variations in the finished height of each pressed body. The need to precisely regulate the pressing force, in explosives production, currently requires that each body be pressed separately.
In addition, in the large scale presses necessary to produce the required pressing force, it is impossible to make the axes of the rams travel in perfect alignment with the axis of the die when the rams are rigidly bolted to the platens. Even when the platens are adjusted to near-perfect parallelism, attempts to do this inevitably result in destructive galling as the rams rub on or dig into the walls of the die, proportionate with the degree of misalignment between the platen guide columns and the axis of the die. If galling occurs with a charge of explosive molding powder, it is likely to initiate the explosive, producing a destructive accident. Therefore some degree of mechanical freedom must be devised for the rams to maintain alignment with the die in the horizontal plane as they engage the die in the vertical direction. This problem has already been addressed by prior tooling for single position pressing. FIG. 2 illustrates prior art for an existing press ram floating adaptor, which allows for automatic horizontal adjustment of the position of the ram.
The conventional method has always been to install and actuate a single set of tooling. The presses available to general industry (which have been adapted to explosives processing) are designed for single position tooling sets. They have no capability to exactly divide the pressing forces among multiple position tooling sets. The operation of compressing explosives to the desired size and density is time consuming and it would be an advantage to use multiple position tool sets to compress multiple bodies of explosives in a single operation of the press. There is a need for an improvement to the hydraulic press to accommodate multiple tool sets with control to exactly divide and distribute the press force exerted on each of the tool sets. There is also a need for an improvement to the hydraulic press to provide some degree of automatic axial adjustment of the ram positions, to compensate for minor misalignment of the ram and die's vertical axes and prevent destructive tool damage.